What do superbrands want with Alicia Keys, Marc Jacobs and Victoria Beckham?

It used to be enough for famous people to appear in adverts and be paid to endorse products or be seen using them in their own, fabulous lives. Now, in the ultimate merging of celebrity and corporate cultures, business cards have become the must-have accessory for stars with time on their hands.

Marc Jacobs is the latest name to be appointed a “creative director”, in a year-long appointment with Diet Coke. Why the quotation marks? Because, while neither party has explained precisely what the role will involve (typically Diet Coke’s high-profile designer signings reimagine the bottle that houses the fizzy fuel of the fashion industry), we can only guess at the amount of time the American fashion designer will spend inside Coca-Cola HQ. At least he actually is a designer... Unlike Alicia Keys.

It’s also unclear how many hours Keys will devote to her new role as creative director at Blackberry. The singer said at the firm’s phone launch last week that she would “work closely with the app designers, developers... to really explore the platform and create ideas for its future.” But when, at the end of the press conference, she said to Blackberry chief Thorsten Heins, “I’ll see you in the office,” she laughed when he replied: “Monday at 8am.”

See also: Lady Gaga at Polaroid, Victoria Beckham at Range Rover, and Justin Timberlake, who has been trying to bring sexy back to US firm Callaway Golf since 2011.

Will.i.am insists he clocks on once a month in his role as director of creative innovation, no less, at computer chip manufacturer, Intel. “I say, ‘This is the behavior now, this is the culture now, so the chip should be like this,” the rapper and producer said in an interview in Details Magazine.

Whatever they’re doing, why are they doing it, and what do real creative directors think about celebrity encroachment?

Yan Elliot, former creative director at ad agencies Mother and WCRS, and founding partner at Fabula, is, surprisingly, pro. “I do wonder what involvement there really is but, as marketing people we can get very bogged down in our own little world,” he says. “It’s good to get advice and perspective from someone who’s pure talent.”

As Elliot points out, big names in music used to resist selling out at all costs. But jobs rather than endorsements can join brands in marketing symbiosis that can give both what they crave: coolness by association; business chops; money.

Not all creatives are keen, however. “I thought the question was a gag,” Geore Lois, the veteran US ad man told Details when asked about the trend. “And when I realized the likes of Justin Timberlake and Lady Gaga were being ordained celebrity creative directors, I gagged... calling them that is an insult to real creative directors.”